How to send a string to the web by using coin acceptor signal as trigger?
Arduino do have a board with Wifi (https://www.arduino.cc/en/Guide/ArduinoUnoWiFi), but most Arduino boards don’t have functionality that would allow them to connect to the Internet (web). People either use additional WiFi circuit boards (shields) for this purpose, which they control from the Arduino, or they use a different board that has WiFi on the board such as the ESP8266 or more recent ESP32. You can find a great number of these on the Arduino website under Internet of Things (IoT) section here: https://www.arduino.cc/en/Main/Products
What board or shield did you have in mind?
the available boards i have is NodeMcu and ESP 8266 01